As blood flow is one of the most important physiological indicators, methods for dynamic monitoring of blood flow are of great interest in a wide range of applications and diseases. Optical techniques based on dynamic light scattering comprise a large number of the available methods for blood flow monitoring such as laser Doppler, speckle contrast imaging, and photon correlation spectroscopy. Although all these techniques differ in their measurement geometry and analysis, each is based on dynamic light scattering. Laser Doppler flowmetry is a well-established technique for measuring blood flow, although it is usually limited to measurements at single spatial locations. More recently, laser speckle contrast imaging (LSCI) has become widely used to image blood flow in a variety of tissues. Because LSCI enables full-field imaging of surface blood flow using simple instrumentation, it has distinct advantages over techniques such as laser Doppler flowmetry. Although the instrumentation for LSCI is simple, obtaining quantitative measures of blood flow can be challenging due to the complex physics that relate the measured quantities to the underlying blood flow.
The advantages of LSCI have created considerable interest in its application to the study of blood perfusion in tissues such as the retina and the cerebral cortices. In particular, functional activation and spreading depolarizations in the cerebral cortices have been explored using LSCI. The high spatial and temporal resolution capabilities of LSCI are incredibly useful for the study of surface perfusion in the cerebral cortices because perfusion varies between small regions of space and over short intervals of time.
One criticism of LSCI is that images are produced slower than real-time. Due to the limited time available during biomedical imaging procedures, it is essential to increase the speed by which the images are produced. Delayed image production is a serious problem, leading to incomplete measurements and improper diagnoses. Regrettably, the processing of laser speckle contrast images has previously required about a second to process a frame while acquisition can occur at rates exceeding 100 frames per second. Consequently, the processing speed of laser speckle contrast images hinders complete use of the available temporal resolution.